Member #1679

Please remove references to MPPT, this chip does not actually do MPPT! The reference point is hardwired in, and assumes a maximum input voltage under full sun conditions. The only way to do true MPPT is to periodically let the solar panel voltage float open circuit (while running from battery) and then load the solar panel at ~80% of that open circuit voltage. Otherwise you are not getting maximum power from your solar panel. This is what the BQ25570 does, please use it instead!

I have experience with an array of up to 10 cells in parallel in 0.01C type applications and they do not have balancing issues as far as I can tell simply because the voltage is drawn down simultaneously on all cells. They are essentially self leveling, where the stronger cells feed the weaker cells until becoming equivalent. I have never used series arrays but that seems like trying to balance a house of cards. A single cell charger is all that is needed to charge a parallel array. Depending on your application, a protection circuit on each cell would help stop the whole array from exploding if 1 battery fails short. Keep in mind that the initial current draw from a fully charged array will be sourced heavily from the strongest battery in array so high current draws on a freshly charged pack could be problematic, but the heavy load from the single cell should not last long as the cell voltages become equivalent. Maybe someone else can speak to heavy loads on parallel arrays.

It seems that series arrays would be much more dangerous because of reverse charge issues that simply aren’t possible on parallel arrays and higher currents that naturally occur as a result of higher voltage. Parallel arrays distribute the current load and as the battery resistance imbalance increases, rather than reverse charge, the pack simply won’t last as long.

I don’t disagree that Sparkfun is a great company, but they are going overboard with this idealogy hurting the real innovators, who are their customers. Sparkfun is a tools company. They assemble tools that other people/companies use to develop products. They are not affected by patent trolls since they don’t create innovative products that can be patented. If Sparkfun were to do a customer survey as to why their customers buy their products, they would likely find many entrepreneurs who need to acquire building blocks to make innovative products. Stop preaching about something you don’t understand. You may be bolstered by hobbyists, but not by those trying to make a living in electronics.

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